After nearly four decades of continued interest and research, silicon micromechanical resonators/oscillators are finally being commercialized for timing and frequency control applications. Among the many available transduction schemes for silicon microresonators, piezoelectric and capacitive mechanisms have been extensively explored over the years due to their individual superior performances. While the former offers lower motional impedance and relative ease of fabrication, the latter offers a very high fQ (resonance frequency×quality factor) product that translates to low-jitter in oscillators and high-precision in resonant sensor systems. However, the additional circuitry needed to generate the DC polarization voltage (Vp) for capacitive actuation renders such oscillators and sensor systems incompatible with low voltage processes. One approach to alleviate the need for an externally-applied DC voltage is to use the resonant silicon microstructures suspended on the oxide layer of a Silicon on insulator (SOI) as capacitors to store charges. However, a DC bias source is still needed to start-up the resonator and to intermittently replenish the leaked charges.
Accordingly, there is a need for capacitive mechanism solutions that do not require an externally-applied DC voltage or DC bias source.